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480

M

ASTOVSKA

ET AL

.

J

OURNAL OF

AOAC I

NTERNATIONAL

V

OL

. 98, N

O

. 2, 2015

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used to interpolate the analyte concentration.

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) The third step was a test of the solvent evaporation where

participants determined absolute recoveries of both PAHs and

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solution in ethyl acetate and reconstitution in isooctane and

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naphthalene, and & QDSKWKDOHQH KDG WR EH DERYH

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) The fourth step was the determination of the elution

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or could be obtained commercially from different vendors. The

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in different amounts of water in the silica thus potentially

different retention characteristics. Therefore, it is important

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optimum volume of the elution solvent to ensure adequate

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them to dryness.

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used instead of the sample. The concentrations of all analytes

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lowest calibration level standard. For naphthalene, levels below

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naphthalene in the sample) were still acceptable if the source of

contamination could not be eliminated, such as by selection of

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evaporation, etc.

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that were both supplied to them. The samples were spiked at

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requirement established for the study) to test instrument

sensitivity and method precision. The shrimp matrix had to

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) The seventh step was the analysis of practice samples.

Three practice samples were supplied to the participants.

Two of the three samples were shrimp blank matrix already

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Quality Assurance

The method uses a mixture of isotopically labeled & 3$+

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lower concentration levels, a limited calibration curve (without

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calibration standard concentrations, and analyte concentrations,

the collaborators were also required to report ion ratios as a

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of the blank mussel and oyster matrixes were spiked with

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Data Reporting

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conditions, evaporation equipment and conditions, and silica

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were asked to record all observations and any potential method

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preparation or contamination), and have all the results and